Nonaqueous electrolyte secondary batteries such as a lithium secondary battery are currently in wide use as (i) batteries for devices such as a personal computer, a mobile telephone, and a portable information terminal or (ii) on-vehicle batteries.
An example of a separator known to be used for such a nonaqueous electrolyte secondary battery is a laminated separator in which a porous layer containing a filler and a resin is disposed on at least one surface of a porous base material containing polyolefin as a main component.
For example, Patent Literature 1 discloses that a microporous film having (i) compression characteristics such as a particular compression deformation amount and a particular compression deformation growth rate and (ii) a particular pore ratio (porosity) can be used as a battery separator which is excellent in an output characteristic and durability of a battery.